~1800 DNS requests per hour

[Jacky Koning]

Summary of the bug:
I am recording a stream and I found out through pi-hole logging that FFmpeg is doing ~1800 DNS requests every hour. Basically it looks like FFmpeg does not care about DNS TTL.
How to reproduce:

ffmpeg -i http://tweedekamerlive.download.kpnstreaming.nl/plenairezaal/4500/prog_index.m3u8 -bsf:a aac_adtstoasc -vcodec copy "/tmp/test.mp4"

Please let me know if you need more information.

Thanks,
Jacky

[Steven Liu]

sysctl -a | grep ttl

or this maybe should fix by your system, not ffmpeg

[Jacky Koning]

#sysctl -a | grep ttl
net.ipv4.inet_peer_maxttl = 600
net.ipv4.inet_peer_minttl = 120
net.ipv4.ip_default_ttl = 64

The DNS requests go out every ~10 seconds. 4 each time.

[Cigaes]

This sysclt output means Linux. On Linux, like all real Unix, DNS resolving is done by the libc, not the kernel, so this sysctl output is completely useless ; the DNS TTL has nothing to do with the packets' TTL.

FFmpeg indeed does not care about DNS TTL. In fact, like all normal network applications for Unix, it does not even has access to it. If you want to reduce outgoing queries, you need to install a local cache, either nscd or a real DNS cache.

But remember that each DNS request will likely result in a network connection immediately afterward, so the benefit is limited.

[Jacky Koning]

Alright in that case I will close this ticket.

Thanks for your help.

[gjdfgh]

Note that FFmpeg used to make create new TCP connections for each HLS segment. There is some new code in FFmpeg git master (I think it's even enabled by default) that will usually reuse the TCP connection, making the thing more efficient. Might be worth trying.